Specific, well-characterized antisera to the extracellular matrix glycoprotein tenascin were used. Immunoreactivity was detected in association with dentinal tubules; it was particularly prominent in the tooth crown, and was stronger within matrix than within predentine. In contrast, there was no anti-fibronectin staining in dentinal tubules. In periodontium, anti-tenascin immunoreactivity was stronger in the oral and sulcular gingival epithelia than in the underlying connective tissue, in contrast to the strong staining of connective tissue by anti-fibronectin. The appearance of tenascin immunoreactivity in gingival epithelia indicates that this protein is not exclusively a component of mesenchymal extracellular matrix.